The invention relates to methods and apparatus for testing wells.
After a wellbore has been drilled, testing (e.g., drillstem testing or production testing) may be performed to determine the nature and characteristics of one or more zones of a formation before the well is completed. Characteristics that are tested for include the permeability of a formation, volume and pressure of a reservoir in the formation, fluid content of the reservoir, and other characteristics. To obtain the desired data, fluid samples may be taken as well as measurements made with downhole sensors and other instruments.
One type of testing that may be performed is a closed-chamber drillstem test. In a closed-chamber test, the well is closed in at the surface when producing from the formation under test. Instruments may be positioned downhole and at the surface to make measurements. One advantage offered by closed-chamber testing is that hydrocarbons and other well fluids are not produced to the surface during the test. This alleviates some of the environmental concerns associated with having to burn off or otherwise dispose of hydrocarbons that are produced to the surface. However, conventional closed-chamber testing is limited in its accuracy and completeness due to limited flow of fluids from the formation under test. The amount of fluids that can be produced from the zone under test may be limited by the volume of the closed chamber.
A further issue associated with testing a well is communication of test results to the surface. Some type of mechanism is needed to communicate collected test data to well surface equipment. One possible communications mechanism is to run an electrical cable down the wellbore to the sensors. This, however, may add to the complexity and reduce the reliability of the test string.
A need thus exists for an improved method and apparatus for testing wells.